Systems and methods for disinfection

ABSTRACT

Methods and systems for establishing Taylor-Couette flow in a fluid are provided. Aspects of the disclosed methods and systems incorporate Taylor-Couette flow in combination with a source of radiation to provide more uniform radiation exposure to the fluid and its components. Common problems of non-uniform radiation levels and concentration boundary layer effects in UV reactors are largely eliminated using the methods and devices provided herein. In an exemplary embodiment, the reactor of the present disclosure has a hollow outer cylinder or stator and a rotor positioned therein and smooth walls for both the outer wall of its rotor and the inner wall of the outer cylinder or stator in which the rotor is positioned, the space between which forming the annular fluid gap. In an alternative embodiment, either the surface of the outer wall of the rotor or the surface of the inner wall of the outer cylinder or stator or both wall surfaces could be corrugated or furrowed such that they have a series of alternating peaks and valleys. This “wavy wall” embodiment provides a more uniform dosage to the fluid parcels formed within the annular gap of the reactor than the smooth wall embodiment.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.10/692,983, filed Oct. 24, 2003, now U.S. Pat. No. 7,001,571, thatclaims the benefit of U.S. Provisional Patent Application No. 60/420,985filed on Oct. 24, 2002, and to U.S. Provisional Patent Application No.60/461,326 filed on Apr. 8, 2003, all of which are incorporated byreference in their entirety.

BACKGROUND

1. Technical Field

The present disclosure is related generally to methods and systems formoving fluids, more particularly, methods and systems for generatingfluid flow that increases fluid exposure to an energy source forsterilization or disinfection.

2. Related Art

Water use is a major environmental concern and methods to reduce andreuse water consumption are in demand. In food processing facilities,water shortages have made water reclamation and reuse an integralcomponent of environmental programs. To ensure that re-used effluents donot pose an unreasonable risk to public health, the EnvironmentalProtection Agency (EPA) has outlined strict regulations for waterreclamation. These water disinfection regulations provide a substantialpublic health benefit by reducing discharges of many waterbornepathogenic organisms to water supplies, recreational water, shellfishwater and other waters that can potentially transmit disease to humans.

Many technologies exist for bacterial destruction in water reclamationsuch as chlorination which is a relatively low cost disinfectionprocess. Chlorine treatment, however, presents a number of problems. Forexample, chlorine disinfection is incapable of achieving appreciableinactivation of the several viruses and protozoa, specifically,Cryptosporidium parvum at reasonable disinfectant doses and contacttimes (Sobsey, M. D. (1989). Inactivation of health-relatedmicroorganisms in water by disinfection processes. Wat Sci. Tech.21:179-195). In addition, large chlorine concentrations generatechloro-organic, disinfection by-products such as trihalomethanes (THMs)and other carcinogens that persist in the environment (Matsunaga, T.,and M. Qkochi. (1995). TiO ₂-Mediated Photochemical Disinfection ofEscherichia coli Using Optical Fiber. Environ. Sci. Technol.29:501-505).

Due to the environmental concerns associated with chemical disinfection,current water treatment methods are moving away from traditionalchemical to physical procedures (Cho, I. H. et al. (2002). Disinfectioneffects E. coli using TiO ₂ AJV and solar light system. Wat. Sci. andTech. 2: 181-190). For example, use of ultraviolet (UV) radiation isbecoming more popular for wastewater treatment since it is effectiveagainst both bacteria and viruses, leaves no residues and is economical(Wong, E. et al. (1998). Reduction of Escherichia coli and Salmonellasenftenberg on pork skin and pork muscle using ultraviolet light. FoodMicrobiology. 15:415-423). UV processing uses radiation in thegermicidal range from 200 to 280 nm to generate DNA mutations withinpathogens (Federal Department of Agriculture and Center for Food Safetyand Applied Nutrition. (2000). Kinetics of microbial inactivation foralternative food processing technologies. Ultra-violet light). Thelatter study also concludes that to achieve microbial inactivation, theUV radiant exposure must be at least 400 J/m² in all parts of theproduct. Moreover, UV irradiation is particularly effective when it isused in conjunction with powerful oxidizing agents such as ozone andhydrogen peroxide.

Treatment of fluid flow is also important in food processing for examplein processing of beverages such as milk, juices, alcoholic drinks orsoft drinks. Existing methods for treating fluid foodstuffs typicallyinclude exposing the foodstuffs to high temperatures in an effort toneutralize potentially harmful bacteria. Unfortunately, thermaltreatment of foodstuff can cause the breakdown of ingredients includingproteins and vitamins. The United States Food and Drug Administration(US-FDA) has recently published a ruling (21 CFR 179) that approves theuse of UV radiation in place of pasteurization.

Early modeling of disinfection efficiencies in flow-through UV reactorsfocused on the ideal designs of either a completely mixed (stirred tank)or plug flow configurations (Haas, C. N. and Sakellaropoulos, G. P.(1979). Rational analysis of ultraviolet disinfection reactors,Proceedings of the National Conference on Environmental Engineering,American Society of Civil Engineering, Washington, D.C.; Severin, B. F.et al. (1984) Kinetic modeling of UV disinfection of water. Inactivationkinetics in a flow-through UV reactor, J WPCF. 56:164-169). Assummarized by the Water Environment Federation (Water EnvironmentFederation (1996). Wastewater Disinfection Manual of Practice FD-10,chapter 7, Alexander, Va.), Scheible (Scheible, O. K. (1987).Development of a rationally based design protocol for the ultravioletdisinfection process. J. Water Pollution Control Fed. 59:25-31)developed a model to account for non-ideal reactor theory that requiresfour empirical constants. A strictly empirical model was also proposedby Emerick and Darby (Emerick, R. W. and Darby J. L. (1993). Ultravioletlight disinfection of secondary effluents: predicting performance basedon water quality parameters. Proc. Plann. Des. and Oper. EffluentDisinfection Syst. Spec. Conf., Water Environment Federation, Whippany,N.J., p. 187) to account for a number of factors that influence waterquality. Recently, computational fluid dynamic (CFD) solutions haveprovided insight into the turbulent flow characteristics of UV reactors(Lyn, D. A. et al. in E.R. (1999). Numerical Modeling of flow anddisinfection in UV disinfection channels, J Environ. Eng. 125, 17-26).

Of the two ideal designs and considering a single reaction, it is wellestablished that plug flow provides comparable yield but with asubstantial reduction in holdup volume that can exceed two orders ofmagnitude compared to a completely mixed reactor (Levenspiel, O. (1972).Chemical Reaction Engineering, 2^(nd) Ed., John Wiley and Sons, Inc.,New York, N.Y.). For such plug flow designs, the surface-to-volume ratiois large which is favorable to the transmission of UV radiation throughthe reactor walls and contained fluid. The major limitations to plugflow designs, however, are both non-uniform radiation intensities withinthe fluid and low concentrations of absorbing species such as viablepathogens near irradiated walls. The effects of the latter are reducedby increasing the flow rate thus reducing the velocity and concentrationboundary layer thickness but, unfortunately, also the residence time andthus the radiation dosage.

Previous studies on the effects of radiation in Taylor-Couette flow arethe growth of algae (Miller, R. L. et al. (1964). Hydromechanical methodto increase efficiency of algal photosynthesis, Ind. Engng. Chem.Process Des. Dev. 3:134) and the development of a reactor forheterogeneous photocatalysis (Sczechowski, J. G. et al. (1995). A Taylorvortex reactor for heterogeneous photocatalysis, Chem. Eng. Sci.50:3163).

Recently, the inventors herein (Forney, L. J., and Pierson J. A.,(2003), Optimum photolysis in Taylor-Couette flow, AIChE 1.49:727-733;Forney, L. J. and Pierson, J. A. (2003), Photolylic reactors: similitudein Taylor-Couette and channel flows, AIChE J. 49:1285-1292, both ofwhich are incorporated by reference in their entirety as if fully setforth herein) considered a fast photolytic reaction and demonstratedthat optimum photoefficiencies could be achieved if the radiationpenetration depth were controlled in relation to the velocity, boundarylayer thickness. Their latter work also provided a scaling law for theyield in both Taylor-Couette and channel flows.

Thus, there is a need for systems and methods for the non-thermalprocessing of fluids.

There is another need for systems and methods for the non-thermalcontrol of micro-organisms in edible fluids.

SUMMARY

Methods and systems for meeting the aforementioned needs are provided,More particularly, methods and systems for establishing Taylor-Couetteflow in a fluid are provided to address said needs. Aspects of themethods and systems are useful for the irradiation of microorganisms inthe fluid. Exemplary methods and systems incorporate Taylor-Couette flowin combination with a source of radiation. Such a combination canprovide more uniform radiation exposure to the fluid and components ofthe fluid.

One aspect provides a method and system for disinfecting a fluid thatincludes introducing a fluid containing an organism, for example amicro-organism, into a reactor. The reactor typically includes a rotorhaving an outer wall. The rotor is housed within an outer cylinder. Theouter cylinder includes an inner annular wall. The outer wall of therotor and the inner wall of the outer cylinder define a first annularchannel or gap. The outer cylinder also includes an inlet and an outletin fluid communication with the annular channel or gap. Anelectromagnetic energy source is associated with the outer cylinder forirradiating the fluid in the annular channel or gap with ananti-microbial amount of electromagnetic energy. When the reactor isfilled with fluid to be sterilized or disinfected, the rotor speed iscontrolled to create laminar Taylor Couette flow (laminar vortices) inthe fluid in the annular channel or gap. The rotor speed can beregulated with a controller that can vary the rotation of the rotor toform laminar vortices in the fluid, for example inducing Taylor numbersin the fluid of about 40 to about 400. Controllers are known in the artand conventional controllers can be used so long as they can control therotor to induce laminar vortices or Taylor numbers of about 40 to about400. A further embodiment includes a second annular channel or gapinterior of the outer wall of the rotor providing a second annularchannel or gap for receiving the fluid. The first and second annularchannels being in communication with each other.

An exemplary method for irradiating a fluid includes inducing Taylorvortices in a fluid containing an organism, for example by generating aTaylor number in the fluid of between about 40 to about 400(representing laminar Taylor vortices); and irradiating the fluid withan anti-microbial amount of energy. The anti-microbial amount of energycan be ultraviolet light in an amount sufficient to kill or inhibitmicrobial growth in the fluid or render the fluid safe for humanconsumption. Suitable fluids include, but are not limited to, foodstuffssuch as beverages, milk, juice, soft drinks, or alcoholic beverages, andwaste water. In another embodiment, the ratio of the penetration depthof the energy to the velocity boundary layer thickness in the fluid isless than about 1, more preferably from about 0.5 to about 1.

Other systems, methods, features, and advantages of the presentinvention will be or become apparent to one with skill in the art uponexamination of the following drawings and detailed description. It isintended that all such additional systems, methods, features, andadvantages be included within this description, be within the scope ofthe present invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE FIGURES

Many aspects of the present disclosure can be better understood withreference to the following drawings. The components in the drawings arenot necessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present invention. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1A is an illustration of Taylor vortices between two concentriccylinders. Inner cylinder rotating, outer cylinder at rest; d—width ofannular gap; L—cylinder; R=cylinder radius.

FIG. 1B is an expanded view of Taylor vortices of FIG. 1A.

FIG. 2 is cross-sectional view of an exemplary embodiment of a system ofthe present disclosure for disinfecting or sterilizing a fluid includingTaylor-Couette reactor.

FIGS. 3A and B are cross sections of an exemplary Taylor-Couette reactorof the present disclosure showing symmetric (FIG. 3A) and groupedirradiating lamp configurations (FIG. 3B).

FIG. 4 is a cross section of another embodiment of the presentdisclosure.

FIG. 5 is a diagram of a square reaction channel.

FIG. 6 is a line graph showing E. coli inactivation versus Taylornumber.

FIG. 7 is a line graph showing E. coli inactivation versus flow rate forvarious Taylor numbers. Ta=0 corresponds to flow between concentriccylinders.

FIG. 8 is a line graph showing E. coli inactivation versus flow rate forsymmetric and grouped lamp configurations. Ta=0 corresponds to flowbetween concentric cylinders.

FIG. 9 is a line graph showing E. coli inactivation versus flow rate forsymmetric and grouped lamp configurations. Ta=100 corresponds toTaylor-Couette flow.

FIG. 10 is a line graph showing fractional E. coli inactivation versusUV dosage.

FIG. 11 is a line graph showing fractional E. coli inactivation versusdimensionless UV dosage for Taylor-Couette flow; n is the correctionfactor for the effects of the concentration boundary layer; m is theratio of the average fluid UV intensity-to-the intensity at the quartzlamp surface; I_(o) is the average UV intensity at the lamp surface; Kis the inactivation rate constant for E. coli.

FIG. 12 is a line graph showing fractional E. coli inactivation versusdimensionless UV dosage for Taylor-Couette flow (Ta=100). The flowbetween concentric cylinders (Ta=0) and channel flow. Parameters are thesame as in FIG. 11.

FIG. 13 is a line graph showing the percent change in outlet triiodideconcentration versus the ratio of radiation penetration depth tovelocity boundary layer thickness.

FIGS. 14(a) and (b) are schematics of alternative embodiments of thereactor of the present disclosure, FIG. 14(a) illustrating a “wavyrotor” design and FIG. 14(b) illustrating a smooth reactor wall design.

FIGS. 15(a) and (b) illustrate simulated flow patterns for the “wavyrotor” design of FIG. 14(a) assuming Taylor numbers, Ta=0 and Ta=100,respectively.

FIG. 16 illustrates simulated photon dosage for the reactor embodimentsof FIGS. 14(a) and (b).

DETAILED DESCRIPTION

Embodiments of the present disclosure provide methods and systems forproducing Taylor-Couette flow in a fluid. The fluid can be exposed to anenergy source, for example an electromagnetic energy source such as anultraviolet light emitting lamp or other non-thermal energy source.Suitable WV lamps emit radiation in the range of about 200-400 nm,preferably about 200-280 nm. The exposure of the fluid to the energysource can also catalyze a chemical reaction in the fluid or incomponents of the fluid. One embodiment provides a system and method ofirradiating a fluid in the absence of a catalyst. Additionally,irradiating the fluid with energy can kill or inhibit the growth oforganisms such as microorganisms, in the fluid. The term “organism”includes single and multicellular animals, viruses, protozoa, bacteria,fungi, pathogens, and the like.

In one embodiment, the flow characteristics of the fluid approach thatof plug flow but with a residence time that is uncoupled from thehydrodynamics or boundary layer characteristics. For example, oneexemplary system of the present invention includes an inner cylinderthat rotates within a stationary but larger outer cylinder as shown inFIG. 2 (Schlichting, H. (1979) Boundary Layer Theory, 7^(th) Ed.McGraw-Hill Book Co, NY). At low rotation rates a laminar, hydrodynamicconfiguration called Taylor-Couette flow is established consisting of asystem of circumferential vortices within the annular fluid gap. Thelatter constitutes a spatially periodic flow that is the hydrodynamicequivalent to cross flow over a tube bank or lamp array. These vorticesprovide radial mixing, reduce the boundary layer thickness and areindependent of the axial flow rate and thus the fluid residence time. Anadditional feature of the rotating design is the repetitive exposure ofthe fluid parcels to a minimum number of energy sources, for examplelamps, which substantially reduces the maintenance requirements. Thisrepetitive exposure also provides a cumulative exposure to radiationmore efficiently and effectively than the application of a single dose.A further embodiment provides systems and methods for irradiating afluid by inducing laminar vortices in the fluid, for example by inducingfluid Taylor numbers in the range of about 40 to about 400. Laminarvortices can be formed in the fluid by introducing the fluid into thedisclosed reactors, for example a reactor having a rotor within a hollowcylinder.

An exemplary reactor is shown in FIG. 2. The reactor includes rotor 205positioned within an inner hollow of an outer cylinder 240. An annularfluid gap 215 is formed between the inner cylinder of rotor 205. Whenthe rotor rotates within the inner hollow of outer cylinder 240,Taylor-Couette flow is produced in the fluid within annular fluid gap215. The rotor speed can be regulated with a controller 245 that canvary the rotation of the rotor to form laminar vortices in the fluid,for example inducing Taylor numbers in the fluid of about 40 to about400. Controllers are known in the art and conventional controllers canbe used so long as they can control the rotor to induce laminar vorticesor Taylor numbers of about 40 to about 400. The circumferential vortices110 produced in the fluid cause parcels in the fluid to rotate as shownin FIGS. 1A and 1B. The rotation of the parcels permits the parcels tobe repeatedly exposed, for example, to an energy source 220. To maximizethe exposure of energy, such as ultraviolet light, to the parcels, areflector 225 can be placed around the exterior surface of energy source220 to redirect scattered energy into the fluid. The reflector can bemade of any reflective material including metals such as aluminum, tin,silver, glass, or a conventional mirror. The outer cylinder typicallyhas walls 210 composed of material that enables energy such asultraviolet light to pass therethrough without an appreciable loss ofenergy due to absorption, refraction, or reflection. Suitable wallmaterial includes quartz, glass, and synthetic polymers, and may includeany transparent medium.

Fluid enters the reactor via inlet 235, which is optionally positionedat the base of outer cylinder 240. When rotor 205 is actuated to beginrotating, Taylor-Couette flow is established. Fluid exits the reactorthrough outlet 230, optionally positioned at or near the top of outercylinder 240. The fluid can be any fluid including water, solutions,bodily fluids such as blood and the like, wastewater, effluent, washwater, and other waste water, or fluid foodstuffs including, but notlimited to milk, juice, soft drinks, nutrient drinks, diet supplements,and alcoholic drinks etc. The fluid can be irradiated by the energysource to facilitate chemical reactions in or with the fluid.Alternatively, irradiation of the fluid with energy from energy source220 can serve to disinfect or sterilize the fluid. In one embodiment,the irradiation energy is not in the form of heat. Embodiments of thepresent invention advantageously preserve the activity of endogenousnutrients and enzymes in the fluid by using anti-microbial amounts ofnon-thermal energy.

In another embodiment, at least one energy source 220 is positionedtangentially to the outer cylinder wall 210. Suitable energy sourcesinclude electromagnetic energy sources including microwave energysources, ultraviolet light sources, sound wave sources, visible lightsources, infra-red light sources, X-ray sources, gamma ray sources,electron sources, atomic and sub-atomic particle sources, and the like.FIG. 3A illustrates another exemplary embodiment of the reactor having aplurality of energy sources 220 positioned equidistant (symmetrically)around the outer cylinder 210. It will be appreciated that the energysources can be placed in any position around the annular fluid gap 215such that the energy emitted from the energy source 220 is directed intothe fluid in the annular fluid gap 215. FIG. 3B shows a plurality ofenergy sources 220 grouped together and positioned opposite inlet 235.

FIG. 4 is a cross-sectional side view of still another embodiment of thepresent disclosure. In this embodiment, fluid enters the reactor throughinlet 450 which is in fluid communication with an annular channel 405.Inner annular channel 405 is in fluid communication with inner hollow445. The reactor includes rotor 405 having an annular channel 440between an outer wall 410 and an inner cylinder 415. Rotor 405 is housedor positioned within outer cylinder 240 such that the outer wall 410 ofrotor 405 separates annular channel 405.

Outer cylinder 455 includes an inner annular wall 420 defining acircular hollow 445 for receiving inner cylinder 415 of rotor 405. Outerannular wall 460 defines annular channel 405 between outer annular wall460 and inner annular wall 420. Annular channel 405 receives outer wall410 of rotor 405. Annular wall 420 also separates annular channel 440when rotor 405 is positioned within outer cylinder 455. Fluid traversesthrough the annular channels and exits through outlet 430. Outlet 430 isoptionally positioned at the base of outer cylinder 455, for example inthe center of the base of outer cylinder 455 and opposite inner cylinder415. As the fluid traverses the annular channels, it is moved throughmultiple circumferential vortices exposing the fluid and particles inthe fluid to energy source 425. The design illustrated in FIG. 4 hasthree continuous fluid channels of equal length. This design allows forthe same number of vortices as a design having a single annular channelthree times the height as one of the channels of FIG. 4. The design ofFIG. 4 allows for a shorter rotor and reactor. Alternatively, two ormore annular channels can be provided.

Energy source 425 can be integral with annular walls 460, 410, 420, or acombination thereof. Alternatively, energy source 425 can be removablyaffixed to annular walls 460, 410, 420, or a combination thereof or canform all or part of the walls. Energy from energy source 425, such asultraviolet light, can irradiate fluid as the fluid traverses annularchannels 405 and 440. Taylor vortices 110 formed in the annular channelswhen the rotor is actuated cause the fluid and components in the fluidto rotate as shown in FIGS. 1A and 1B and increase the exposure of thefluid and components of the fluid to energy source 425.

The effects of flow rate, energy source location and cylinder rotationrate were considered for the inactivation of bacteria, for exampleEscherichia coli. These results are compared with similar data in aconventional channel. Details of the correlation of the data are alsoprovided based on assumed inactivation kinetics and a plug flow reactormaterial balance. The latter analysis also introduces a new correctionfactor that accounts for the important boundary layer effects.

Another embodiment provides a Taylor-Couette reactor that providesexcellent liquid surface renewal for the application of electromagneticwaves to chemical processing. The photoefficiency of such processes isaffected by the penetration depth of radiation into the fluid relativeto the velocity boundary layer thickness. The secondary flow caused bythe presence of laminar vortices decreases the boundary layer thicknessso that the dosage of radiation is substantially increased for fluidswith large radiation absorptivities. In another embodiment, the maximumphotoefficiencies occur when the radiation penetration depth is equal tothe boundary layer thickness.

Materials and Methods

Bacterial Culture

The Escherichia coli was obtained from the American Type CultureCollection, culture number 15597 (Manassas, Va.), The E. coli culturewas grown and maintained on tryptic soy agar (TSA; Difco Laboratories)and tryptic soy broth (TSB; Difco Laboratories). E. coli was asepticallyrehydrated using plates containing ATTC medium 271 agar at 37° C. for 24hours. Colonies were transferred to agar slants and refrigerated at 4°C. For each experiment, colonies were aseptically transferred to atest-tube containing 10 mL Acumedia 7164A Tryptic Soy Broth. Test-tubeswere placed in a Fisher Versa-Bath-S Model 224 temperature waterbath for24 hr (37° C. and 30 rpm agitation rate). One mL of broth solution wasdiluted to 1-liter deionized water to obtain the 10⁶ CFU/mL influent.

Wastewater

To mimic the bacterial load in wastewater, simulated wastewater wasspiked with 10⁶ CFU/mL of the indicator organism Escherichia coli. Thewastewater was sampled and E. coli colonies were enumerated on trypticsoy agar in order to determine E. coli survival. To simulate wastewater,bentonite which is a colloidal silica of specific gravity of about 2.0was added to establish a total suspended solids (TSS) concentration andturbidity, with full transmittance (FT) values no less than 55%,turbidity less than 2 to 3 NTU, and TSS less than 5 mg/L.

Taylor-Couette Flow

A Taylor vortex column was constructed of 4.6 cm internal diameter,fused quartz stator (Vycor) with a teflon rotor of 3.8 cm diameter by 13cm in length as shown in FIG. 2. The resulting annular gap width d was0.4 cm. The inlet consisted of one 6 mm tube located 13 mm from thebottom of the reactor. The irradiated holdup volume within the annulargap was 16.2 ml. Flow rates were varied from 13.1 to 136.8 ml/min. witha positive displacement pump. Four cold cathode, low pressure mercuryUVC lamps with effective lengths of 3.1 cm [Gilway Technical Lamp. 2001.catalog # 169.] were positioned equidistant around the outer quartzstator. In a second configuration the lamps were grouped 180 degreesfrom the inlet such that adjacent lamps were separated by a distance ofapproximately 2 mm as shown in FIG. 3B.

Lamps were surrounded with an aluminum reflector 225 as shown in FIG. 2.Lamp output (mW) was determined with an International Light IL1471Agermicidal radiometer system (IL1400A monitor and SEL240/QNDS2/TDsensor) providing a spectral range of 185-310 nm and a measurement rangeof 33 μW/cm² to 330 mW/cm². Lamp intensity (mW/cm²) was measured afterlamps were energized for 20-minutes. When all four lamps were placed onthe sensor with an aluminum reflector background, the intensity for thesensor area was recorded as 4.85 mW/cm². The intensity for all fourlamps was further recorded as 4.0 mW/cm² at 1 cm from the sensorsurface. The intensity of radiation for each lamp (wavelength˜254 nm)was therefore rated at about 1 mW/cm at one cm from the lamp center.

The angular rotation of the rotor was controlled by a permanent magnetDC motor providing Taylor numbers over a range from 0<Ta<1000 whereTa=[Ud(d/R)^(1/2)]/ν. Here, U=ωR is the rotor surface velocity, theangular frequency to ω=2πf, f is the rotor frequency, R is the rotorradius, d is the gap width and ν is the kinematic viscosity of thefluid.

Channel

A continuous flow reactor channel 500, 18.5 cm in length, including twoPVC flow straighteners at both ends was constructed from a bronze 2×2 cmID square. Centered in the channel 520 was a fused quartz capillary tube510 as shown in the cross section of FIG. 5. The quartz tube 510 holdsone cold cathode, low pressure, mercury UVC lamp 515 with a totaleffective irradiated length of approximately 7.8 cm. The intensity ofradiation for the lamp (wavelength of about 254=n) was about 1 mW/cm² at1 cm from the center.

The irradiated volume of the reactor was 28.6 ml and the flow ratescovered a range of values from 10<q<40 ml/min. The reactor Reynoldsnumber covered the range 6<Re<25 for the indicated flow rates providingfully developed laminar flow in the cross sectional area. The crosssectional area of the channel is A_(c)=3.9 cm² with a hydraulic diameterof d_(h)=1.52 cm. An estimate of the laminar film thickness isδ=d_(h)/4=0.38 cm that corresponds to the distance to the centerline ofthe asymmetric cross section.

Plug Flow Reactor

The following analysis is an adaptation of that presented by Severin etal. (Severin, B. F. et al. (1984) Kinetic modeling of UV disinfection ofwater. Inactivation kinetics in a flow-through UV reactor, J WPCF.56:164-169) who considered a completely mixed flow-through reactor.Here, we consider a plug flow geometry also of annular design with aradiation source I_(o) at radius r_(o) along the axis. The kinetics ofinactivation are assumed to be first order with respect to both thesurviving organism density and the light intensity. Thus, the localdisinfection rate R becomesR=KI(r)N(r,x)  (1)

-   -   where    -   R=disinfection rate (organisms/cm³-sec)    -   K=rate constant (mW-sec/cni²)⁻¹    -   I(r)=radiation intensity at radius r, and    -   N(r,x)−surviving organism density at radius r and axial position        x (organisms/cm³).

From Lambert's law for a radiation source of infinite length, oneobtainsI(r)=(r _(o) I _(o) r)exp(−E(r−r _(o)))  (2)where I_(o) is the radiation intensity at the quartz tube surface ofradius r_(o), E=2.3 A and A is the solution absorbance.

A local material balance for the surviving organism concentration in anideal plug flow reactor can be approximated in the formq(dN)=−KN(x)I(r)dV  (3)where we have assumed that N is a constant with radius. Here, q is thevolume flow rate and V=π(r_(f) ²−r_(o) ²)L is the volume of the reactorand dV=2πgrdrdx. Substitution of Eq.(2) into Eq.(3) and integrating overr_(o)<r<r_(f), one obtainsdN/N=−mKI _(o) τdx/L  (4)where N=N_(o) at x=0 and τ=V/q is the retention time. Thus, the outletconcentration of surviving organisms becomesN _(f) /N _(o)=exp(−mKI _(o)τ).  (5)The dimensionless factor m in Eq.(5) is the ratio of the average lightintensity in the reactor to the intensity at the surface of the quartztube as derived by Severin et al. (Severin, B. F. et al. (1984) Kineticmodeling of UV disinfection of water. Inactivation kinetics in aflow-through UV reactor, J WPCF. 56:164-169) wherem=2r _(o)[1−exp(−E(r _(f) −r _(o))]/[E(r _(f) ² −r _(o) ²)].  (6)It should be noted that for transparent fluids or E<1.0,m≅2r_(o)/(r_(o)+r_(o)).

If the concentration of surviving organisms N is not constant withradius and a concentration boundary layer exists, then the argument ofthe exponent of Eq.(5) would be reduced by a factor n<1.0. This is theresult of a reduced N in the local disinfection rate of Eq.(1) near theirradiated wall where the radiation intensity is the largest. Thus, oneobtainsN _(f) /N _(o)=exp(−nmKI _(o)τ)  (7)where n is an empirical constant that is independent of axial distancefor fully developed flow. Similar arguments were made in the study ofphotolytic reactions for such laminar plug flow geometries by Forney andPierson (Forney, L J. and Pierson, J A. (2003b), Photolylic reactors:similitude in Taylor-Couette and channel flows, AIChE J. 49:1285-1292)which is incorporated herein in its entirety.

EXAMPLE 1 Taylor Number

Values for the inactivation of E. coli in the Taylor column wererecorded at increasing rotation rates up to roughly 300 rpmcorresponding to a Taylor number of 1000. The data shown in FIG. 6indicate a minimum of a 4-log reduction in surviving E. coli in units ofcolony forming units per ml or cfu/ml at a value of Ta=100 or roughly 30rpm (˜0.5 Hz). Although the value of Ta=100 is somewhat above thecritical value of Ta=41 for the onset of laminar Taylor vortices, Ta=100represented an incremental reduction of roughly 1 or 2-logs in cfu/mlcompared to other values of Ta with comparable flow rates as shown inboth FIGS. 6 and 7. At Ta=400 the vortices become turbulent and theresidence time distribution of the fluid broadens such that thecharacteristics of the Taylor column approach that of a completely mixedflow-through reactor. For values of 41<Ta<400 in the laminar range thereactor characteristics approach that of ideal plug flow with decreasingTa.

As indicated in FIG. 6 the optimum rotation rate is in the laminar rangeof Ta. At higher rotation rates the bentonite is probably forced to theouter stator surface which in turn absorbs the applied UV radiation. Alldata recorded in the experiment constitute the average of at least twomeasurements of surviving E. coli for fixed operating conditions. Theerror bar for the data point at the minimum in FIG. 6 indicates thevalues for two independent measurements of E. coli. The remaining datawith the same error or uncertainty of roughly 10² cfu/ml per point wasinsignificant compared to the larger concentrations of E. coli on thelog plot. Also recorded in FIG. 6 are the influent concentrations of E.coli along with the expected error. The latter error was determined bymeasuring the E. coli concentrations both before and at the conclusionof the experiments.

EXAMPLE 2 Flow Rate

Values of E. coli inactivation were recorded at increasing flow ratesfor three values of the Taylor number Ta=0, 100 and 120. As indicated inFIG. 7 the inactivation levels decreased with higher flow rates for allvalues of Ta since the radiation dose ∝1/q where q is the volumetricflow rate through the reactor. A value of Ta=100 provides the largestinactivation rates for all recorded flow rates. Significantly, the plotalso indicates an increase of over 2-logs for E. coli inactivationcompared to simple flow through concentric cylinders (Ta=0) for moderateflow rates of 20 to 40 m/min.

EXAMPLE 3 Lamp Symmetry

The effects of lamp location on inactivation were measured and the dataare recorded in FIGS. 8 and 9. FIG. 8 with no rotation or Ta=0demonstrates that channeling of the pathogens occurs between concentriccylinders when the lamps are grouped on the side of the reactor oppositethe fluid inlet.

For the symmetrical case of equidistant lamp location and at Ta=100,FIG. 9 illustrates that an improvement of over a 1-log reduction insurviving organisms was again observed compared to the grouped geometryfor moderate flow rates between 20<q<60 ml/min. Moreover, theimprovement was somewhat less than 1-log at higher flowrates q>60 ml/minat lower photon dosages. One concludes that there is a significant lossof photons from both reflection and transmission through multiple lampsin close proximity,

EXAMPLE 4 Dosage

The inactivation of E. coli was measured for the channel and the dataare compared in FIG. 10 to the results taken with the Taylor column atTa=0 and 100. In FIG. 10 the UV dosage was computed based on the averageradiation intensity within the fluid times the fluid residence time. Thevalue of m defined by Eq.(6) that represents the ratio of averageintensity within the fluid-to-the quartz surface value was estimatedfrom the approximation m=2r_(o)/(r_(o)+r_(f))=0.42 for low fluidabsorbance where rf is equal to the radius of a circle with the samecross sectional area as the square channel in FIG. 5. The correspondingvalues of m for the annular gap in the Taylor column were estimated tobe m=1.0 since the lamps were located outside the gap with photoreflection inward toward the rotor.

The lamp intensity I_(o) in units of mW/cm at the quartz tube surfacefor the channel in FIG. 5 was computed from the lamp length and tubediameter. To compute I_(o), the total mW output from the 7.8 cmeffective lamp length was divided by the quartz tube surface area.Similarly, to compute the average light intensity I₀ of the insidesurface of the quartz stator in the Taylor column, the total lamp outputin mW for 4 lamps with an effective length of 3.1 cm per lamp wasdivided by the total surface area computed from the inside diameter ofthe quartz stator (length of 3.1 cm). The intensity of radiation forboth the channel and the Taylor column were based on an assumedabsorption of 6% for the quartz tube (GE 124) and 27% for the quartzstator (Vycor Corning 7913), respectively.

The results in FIG. 10 indicate more than a 3-log reduction in theinactivation of E. coli with Taylor-Couette flow compared to aconventional channel at moderate flow rates of 20<q<40 ml/min. Theseconclusions are based on an equal radiation dosage in units of mJ/cm²within the fluid.

EXAMPLE 5

One of the major problems that one must contend with during thecontinuous use of UV reactors is the maintenance requirement of bothcleaning the numerous lamp surfaces from fouling and replacement ofdefective lamps. The use of Taylor-Couette flow provides repetitivecontact of fluid parcels with a minimum number of lamps. For example, inone embodiment described herein operating at Ta=100, with four lamps anda flow rate of 20 ml/min, a given fluid parcel will make roughly 25revolutions before reaching the outlet. Therefore, with four lamps perrevolution, a parcel of fluid therefore makes contact with theequivalent of 100 lamps as it passes through the Taylor column.

The optimum inactivation data for Ta=100 with the Taylor column can bereplotted in the form suggested by Eq.(7). The inactivation rateconstant for E. coli or K=0.89 cm²/mW-s that appears in the independentvariable nmKI_(o)τ was substituted from the batch inactivation data from(Severin, B. F. et al. (1984) Kinetic modeling of UV disinfection ofwater. Inactivation kinetics in a flow-through UV reactor, J WPCF.56:164-169). The remaining value of the boundary layer, correctionfactor n can be estimated by comparison with the data. The resultingplot is shown in FIG. 11 which is data replotted from FIG. 10 with avalue of n=0.28 in Eq. 1 that places the theory through the first sixdata points. As illustrated in FIG. 11, all of the fractionalinactivation data appear to conform to the model of a plug flow reactorwith the exception of those data taken at the low flowrates near q=20ml/min on the left of FIG. 10. These latter data are subject to both theeffects of the centrifugal forces leading to an increase in thebentonite concentrations near the transparent stator surface and togravitational settling of the silica colloid at the inlet passage.

In a similar fashion, all of the data of FIG. 10 were replotted in FIG.12 with estimates of the boundary layer, correction factor n for eachcase as shown in the figure caption. Again, all of the data appear toconform to the plug flow model. It is interesting to note that estimatedvalues of n in FIG. 11 appear to decrease with increasing boundary layerthickness. The latter observation conforms to the earlier work ofForney, L. J. and Pierson, J. A. (2003), Photolylic reactors: similitudein Taylor-Couette and channel flows, AIChE J. 49:1285-1292 whichsuggests that the yield from photolytic reactions in fully developedlaminar reactors n∝1/δ where 6 is the velocity boundary layer thicknessor that n∝1/δ in Eq.(7).

Table 1 shows a comparison with the empirical values of n used in FIG.12 with the expression n=0.023/δ. The empirical values of n were chosenin FIG. 12 and Table 1 such that there were an equal number of datapoints both above and below the theory. Moreover, in Table 1 the valuesof the velocity boundary layer thickness 5 were taken from Forney, L. J.and Pierson, J. A. (2003), Photolylic reactors: similitude inTaylor-Couette and channel flows, AIChE J. 49:1285-1292 where 8 wasestimated to be dh/4 for both the channel and the case of flow between aconcentric cylinders (Ta=0) where dh is the hydraulic diameter. Thevalue of 5 for the case Ta=100 was estimated to be on the order ofTa^(−1/2) (Forney, L. J., and Pierson, J. A. (2003) Optimum photolysisin Taylor-Couette flow, AIChE J. 49:727-733).

The common problems of non-uniform radiation levels and concentrationboundary layer effects are largely eliminated in UV reactors with theuse of Taylor-Couette flow that is the hydrodynamic equivalent to crossflow over a tube bank (Baier, G. et al. (1999). Prediction of masstransfer in spatially periodic systems, Chem. Eng. Sci. 54:343) or forthis application a lamp array. Moreover, the repetitive exposure offluid parcels to a small number of lamps decreases maintenancerequirements. Over a 3-log reduction in the inactivation of E. coliunder the best conditions was demonstrated compared to a conventionalchannel with the same radiation dosage. Moreover, greater than a 2-logreduction was evident compared to flow through concentric cylinders.

The inactivation data for three reactor geometries of Taylor-Couetteflow and flow between either concentric cylinders or a square channelare correlated with the assumption of plug flow. In particular, theeffects of non-uniform radiation levels are accounted for by integrationacross the fluid channel as done in the past but a new correction factoris introduced that is inversely proportional to the velocity boundarylayer thickness to account for the effects of a concentration boundarylayer. TABLE 1 Prediction of Boundary Layer Correction Factor-n nBoundary Layer Thickness - empirical Flow Geometry δ(cm) 0.023/δ (FIG.11) Taylor-Couette 0.08 0.28 0.28 Ta = 100 Concentric 0.2 0.11 0.09Cylinders Ta = 0 Channel 0.38 0.06 0.06

EXAMPLE 6 Photochemistry

Fast UV photolysis of aqueous iodide producing triiodide was alsoinvestigated. Concentrated KI solutions are optically opaque atwavelengths of 254 nm and act as photon counters. UV absorption byiodide leads to an aqueous or solvated electron via a chargetransfer-to-solvent reaction and the formation of an excited iodine atomThe essential reactions are listed below,I⁻+hv→I+e⁻  (8)I+e⁻→I⁻  (9)2I*+I⁻→I₃ ⁻  (10)As noted, the UV-induced formation of triiodide is potentially limitedby the back reaction of Eq.(9). The quantum yield for triiodide issignificantly increased, however, by the addition of potassium iodate.In the presence of iodate, scavenging of the bulk electron occurs andthe following additional reaction is proposedIO₃ ⁻+e⁻+2H₂O→IO⁻+H₂0₂+OH*+OH⁻  (11)The yield of the triiodide photoproduct is easily monitored byspectrophotometry at either 350 or 450 nm depending on theconcentration. The quantum yield of φ=0.75 mol./einstein is relativelyconstant with either temperature or reagent iodide concentrations. Withthe addition of a borate buffer (pH 9.25) to minimize thermal oxidation,stock solutions of 0.6 M KI and 0.1M KIO3 with the borate buffer arestable and insensitive to ambient light in the visible spectrum. Radialmass transfer in Taylor-Couette flow has been documented in terms of aSherwood number Sh of the formShαTa^(1/2)Sc^(1/3)  (12)where the Taylor numberTa=(ωRd/ν)(dR)^(1/2)  (13)The indicated exponents in Eq.(12) were determined previously by anumber of experiments and also confirmed by the recent numericalpredictions. The torque coefficient CM for Taylor-Couette flow is of theformC _(M)=2M/(πρω² R ⁴ h)αTa ^(−1/2)  (14)for the range of Taylor numbers Ta_(c)<Ta<400 where the critical Taylornumber Ta_(c)=41 indicates the onset of laminar vortices. Here, themoment M=τ(2πR²) and τ is the shear stress on the rotor.

Equations (12) and (14) suggest that the transport coefficients inlaminar, Taylor-Couette flows are correlated by a Chilton-Colburnanalogy of the formJ _(D) =Sh/(TaSc ^(1/3))=C _(M)/2  (15)For the values 40<Ta<400 and the Schmidt number Sc=ν/D>1, Theseconclusions are consistent with laminar and heat transfer correlationson a spinning disc but with Ta replaced by the Reynolds number based onthe disc angular velocity and diameter.

Consider now a laminar boundary layer with a linear velocity andconcentration profile (film model) on the surface of a Taylor-Couetteflow (Ta>Ta_(c)) Since the mass transfer coefficient k_(c)αD/δ_(c) andthe Sherwood numberShαk_(c)d/D  (16)where δ_(c) is the concentration boundary layer thickness, d is the gapwidth and D is the solute molecular diffusivity, one obtainsShαd/δ_(c)α(d/δ)(δ/δ_(c)).  (17)Since a boundary layer analysis confirmed by experiment suggestsδ_(c)/δαSh^(1/3), one obtains a ratio of characteristic reactor lengthd-to-velocity boundary thicknessd/δαTa^(1/2)  (18)for Ta>Ta_(c).

Attempts to obtain Eq.(18) by stretching the characteristic lengths d orδ for a boundary layer on a flat plate by a factor of (dR)^(1/2) wereunsuccessful. There is some evidence, however, that the Sherwood numberShαTa^(1/2)Sc^(1/3) (d/R)^(0.17) from the mass transfer experiments ofHoleschovsky and Cooney but, again, the exponent magnitude of 0.17 isinconsistent with the attempted boundary analysis that would suggestlarger values.

Fast photochemical reactions must occur near transparent reactor walls.The thickness of the reaction layer, however, is not confined to afraction of the velocity boundary thickness, but rather to the radiationpenetration depth. The latter depth, in fact, can exceed both theboundary thickness or characteristic reaction dimension depending on theabsorbance of the reacting solution.

Since the solution absorbance is defined byA=AεC  (19)where the intensity of radiation is I/I_(o)=10^(−A), ε is the extinctioncoefficient, C is the absorbing species and A, is the radiation depth,the reaction layer is therefore confined to a layer on the order ofAαI/εC.  (20)

An additional dimensional parameter is the maximum possibleconcentration of photochemical product formed. The latter is equal tothe product of the number of photons introduced into the reactor and thequantum efficiency of the reaction. The maximum concentration of productformed is thusCm=nI _(o) A ₁ φ/γq  (21)where n is the number of lamps, I_(o), is the intensity of radiation[W/cm2], A₁ is the area of a single lamp, φ is the reaction quantumefficiency [mol product/einstein], q is the reactor volume flow rate andγ[J/einstein] is the conversion factor from a mol of photons to joulesof energy.

Dimensional arguments suggest that the concentration of photochemicalproduct formed C_(ω) is of the formC_(ω)C_(i)(I)αf(Cm/C_(i)(I), λ/δ)  (22)provided the Taylor number Ta>0 where C_(i)(I) is the concentration ofreactant iodide in the inlet stream. Simplifying Eq.(22) somewhat sincea mass balance implies C_(ω)αCm, one obtainsCω/C_(i)(I)αCm/C_(i)(I)[f(λ/δ)].  (23)Defining Co as the product concentration with no rotation, one nowobtains an expression which isolates the effects of rotation in the formof the dimensionless quantity(Cω−Co)/Co=f(λ/δ)  (24)

Another embodiment provides a Taylor vortex column having a bronze rotor3.43 cm in diameter by 5 cm in length centered within a fused quartzbeaker with an inside diameter of 4.1 cm providing a gap width ofd=0.334 cm. The holdup volume (irradiated) was 12 ml with a range offlow rates between 15<q<50 ml/min. Five cold cathode, low pressuremercury UVC lamps with effective lengths of 3.1 cm were positionedaround the quartz beaker and surrounded by an aluminum reflector with anover 90% reflectivity of UV radiation. The intensity of radiation foreach lamp (wavelength˜254 run) was rated at 1.7 mW/cm2 at the lampsurface providing a range of power input from 0.033 W to 0.164 Wdepending on the number of lamps engaged.

A solution of 0.6 M potassium iodide (KI) and 0.1 M potassium iodate(KIO₃) buffered (pH 9.25) with borate was pumped through the Taylorcolumn. The absorbance of triiodide at the outlet was measured at either350 or 450 run for low or high concentrations, respectively, dependingon the number of lamps engaged or liquid flow rate. The rpm of therotor, controlled by a permanent magnet DC motor, was varied between0<rpm<75 providing a Taylor number covering the range 0<Ta<200.

The triiodide absorbance as expected, clearly indicated a large increaseof roughly 60% for Taylor numbers Ta>Ta_(c) where the lower limit ofTa_(c)=40 corresponds to the onset of Taylor vortices at low axialReynolds numbers. Since the cross sectional area for the flow within thegap is 4 cm², the axial Reynolds number was Re<10 for all experimentsand thus had no effect on the critical Ta_(c).

Plug Flow Reactor

When the Taylor number Ta>Ta_(c) and laminar vortices are present withinthe Taylor column, the flow can best be described as approximating thatof an ideal plug flow reactor. Assuming a zero order rate expression atsteady-state. one obtainsudC/dx=r  (25)where the constant rate[mol/liter-s]r=nI _(o) A ₁ φ/γV  (26)and V is the holdup volume of the reactor Thus, the concentration oftriiodide formed from Eq. (25) with dx/u=dV/q isC(I ₃)=βrV/q  (27)where the factor β<<1 accounts for both the loss of input radiant energyto liquid heating and surface absorption and the effects of backreactions from triiodide to iodide depleting the product as describedlater.

Normalized plots of Eq.(23) for the outlet triiodide concentration forincreasing flow rates at fixed rpm (Ta=100) and the standard stocksolution (0.6 M iodide) where Cm is defined by Eq. (14) show that thephoto efficiency of the reactor is not high (<30%) so that axialvariations in the iodide reactant and thus the radiation penetrationdepth are small consistent with the analysis.

Effects of Rotation

The effects of rotation are isolated by comparing the productconcentration at fixed Taylor numbers Ta>Ta_(c) with the product formedat zero rpm or Ta=0. Because of the large surface-to-volume ratio forthe reactor, one would expect a considerable enhancement in themagnitude of the transport coefficients without vortices. A nearlyconstant 70% improvement in product yield occurs for all Ta>Ta_(c)

Percentage increase in reaction product at fixed Ta=100 for variousvalues of the radiation dosage were obtained by engaging one to five UVlamps and changing the flow rate between 16 and 32 ml/min. There is somescatter in the data possibly due to channeling through the reactor forthe Ta=0 case, since the reactor inlet and outlet were located on thesame side but 45° apart. Thus, the sequence of lamps in thecircumferential direction was varied for several experiments with thesame total power input leading to the indicated scatter. However, it isapparent from the data that the concentration of product formed due torotation is independent of the dosage of radiation supplied as suggestedby Eq. (24).

Optimum Rotation

The similarity law proposed by Eq. (24) was tested by varying thereactant concentration, that is, the concentration of iodide fed to thereactor inlet. Since the absorbance A=λεC_(i)(I) is 200 for a 0.6 M KIand 0.1 M KIO₃ solution, the extinction coefficient e at a wavelength of254 nm was calculated to be ε=333 M⁻¹cm⁻¹. Setting the absorbance A=1that represents a radiation depth over which 90% of the UV photons areabsorbed, one calculates the radiation depth to be λ=1/εC_(i)(I).

The stock solution of 0.6 M KI and 0.1 M KlOs along with a series ofadditional solutions with KI and KlO₃ in the same ratio but diluted by afactor of up to 100 were fed to the reactor. The product triiodideconcentration was measured at both Ta=0 and 100 for each inlet solution.The data show that the reaction yield is inhibited if the reaction layerlies within the velocity boundary layer or λ/δ<<1 (see FIG. 1B). Underthese circumstances the large concentration of I₃ ⁻ within the boundaryis reduced by the solvated electron e_(aq) ⁻ back to I⁻ via the reactione_(aq) ⁻+I₃ ⁻→I₂ ⁻+I⁻  (28)and the product yield of K is diffusion limited.

FIG. 13 shows the percent change in outlet triiodide concentrationversus the ratio of radiation penetration depth to velocity boundarylayer thickness. If the reaction layer thickness is greater than thevelocity boundary layer or λ/δ>>1, the product I₃ ⁻ is formed throughoutthe gap and the advantages of the circulating vortices are substantiallyreduced. It should be noted that the left data point in FIG. 13corresponds to a reaction layer that is 15% of the velocity boundarythickness where the latter is 10% of the gap width d. In contrast, theright data point in FIG. 13 represents a radiation depth that is 150% ofthe gap width d. At the optimum operating conditions λ/δ=1 one obtains amaximum 150% increase in the product concentration. Under the latterconstraint ifλ/δ=Ta ^(1/2)/(dεC _(i)(I))  (29)setting λ/δ=1, one obtains an optimum frequency f_(op) Hz of rotationequal tof _(op)=(ν2π)(dR)^(1/2)ε² C _(i) ²(I)Scale-UP

An efficient UV reactor requires multiple exposure of the pathogen to afixed number of lamps positioned around the reactor circumference. Thenumber of cycles of the pathogen around the axis of the reactor as thepathogen passes from inlet to outlet is N whereN=ft _(r)and f is the rotor frequency (cycles/sec) and t_(r) is the fluidresidence time ort _(r) =V/q=πDdh/qHere, h is the rotor length, d is the gap width, D (=2R, see FIG. 1A) isthe rotor diameter, q is the fluid flowrate and V is the volume of fluidwithin the annular gap. The number of cycles N can be rewritten in theformN=Ta(D/2d)^(1/2) νh/qThus, for fixed Taylor number Ta and gap width d such that the ratio ofradiation penetration depth-to-boundary layer thickness λ/δ is aconstant and for fixed fluid properties ν, one obtainsNαD^(1/2)h/qThus, scale-up of the reactor to larger rotor diameters D and longerrotors h is achieved for fixed N ifqαD^(1/2)hAdditional Reactor Configurations

The reactor described above in connection with, for example, FIG. 2 hasflat or smooth walls for both the rotor 205 and outer cylinder or stator240 that form the annular fluid gap 215. These walls need not be smoothor flat. In an alternative embodiment, one or both walls may becorrugated or furrowed, meaning they are formed into a series ofalternating ridges and grooves.

FIGS. 14A and B illustrate these alternate reactor designs. FIG. 14Bshows the aforementioned reactor of FIG. 2 where the rotor 205 has asmooth or flat outer wall 206, and similarly outer cylinder or stator240 has a smooth or flat inner wall 241. In the alternative embodimentof FIG. 14A, the outer cylinder or stator 640 has a smooth or flat innerwall surface 641, while rotor 605 has a corrugated or furrowed outerwall surface 606. We refer to the configuration of FIG. 14A as the “wavyrotor” embodiment.

The reactor of FIG. 14B has a uniform gap, d, between the smooth outerwall 206 of the rotor and the smooth inner wall 241 of the outercylinder. On the other hand, the wavy rotor reactor design of FIG. 14Ahas non-uniform gap spacing, d, between the outer wall surface 606 ofthe rotor and the inner wall surface 641 of the outer cylinder. Thecorrugated wall surface 606 of this wavy rotor design has alternatingridges and grooves, or peaks and valleys. The outer wall of the wavyrotor can be described as having a gap spacing, d₁, between the smoothinner wall 641 of the outer cylinder and the peaks of the corrugatedwall 606 of the rotor; an average gap spacing, d, between the inner wall641 of the outer cylinder and the average distance between the peaks andvalleys of the corrugated inner wall 606 of the rotor; a wavelength, L,which is the distance between the peaks of the corrugated wall; and awave amplitude, h, which is the distance between the peaks of thecorrugated rotor wall and average of the distance between the peaks andvalleys of the corrugated wall.

Examples of flow patterns of fluid passing through the annular gapformed between the outer corrugated wall of the wavy rotor and the innerwall of the outer cylinder or stator of FIG. 14A, generated by numericalsimulation, are illustrated in FIGS. 15(a) and (b). The simulations ofboth FIGS. 15(a) and (b) are based on the assumption that the wavy rotorhas wavelength, L, of 4 millimeters and a wave amplitude, h, of 1millimeter. FIG. 15(a) is further based on the assumption that theTaylor number, Ta, is zero meaning the rotor has zero rpm. On the otherhand, FIG. 15(b) is based on the assumption of a fixed Taylor number,Ta, equal to 100. As can be seen from the simulation of FIGS. 15(a) and(b), the wavy rotor design increases the vorticity of the fluid passingthrough the annular gap between the rotor 605 and the outer cylinder640, thus improving mixing.

Application of UV radiation through the outer cylinder or stator wall640 into the annular fluid gap between the rotor having a wavy wall ofFIG. 15(a) and the outer cylinder or stator is shown to increase thephoton dosage, D(mJ/cm2) to the fluid parcels illustrated in FIG. 15(b).The simulated increase in photon dosage D for the wavy rotor isillustrated in FIG. 16. The simulated distribution of photon dosage in areactor having the smooth walls of FIG. 14(b) is shown by the curve onthe left in FIG. 16. The simulated or predicted increase in dosage forthe same reactor rotation rate and average fluid gap is illustrated inthe curve on the right of FIG. 16 for the wavy wall embodimentillustrated in FIG. 14(a). In addition to a larger dosage for the wavywall embodiment as compared to the smooth wall embodiment, the wavy wallembodiment provides a more uniform dosage to the fluid parcels asindicated by the increase in the maximum fraction of fluid parcels thatreceive the given dosage on the vertical axis, FIG. 16, from 70 for thesmooth wall embodiment of the curve on the left to 200 for the wavy wallembodiment of the curve on the right. Consistent with the increase inthe height of the dosage distribution for the wavy wall embodiment is adecrease in the width of the dosage distribution indicating a moreuniform dosage for the wavy wall embodiment of FIG. 14(a) than thesmooth wall embodiment of FIG. 14(b). The simulation of FIG. 16 assumesa gap, d, of 2 millimeters for the smooth wall embodiment of FIG. 14(b)and an average gap, d, of 2 millimeters for the wavy wall embodiment ofFIG. 14(a). The wavy wall embodiment is also assumed to have gapspacing, d₁, between the peaks of the wavy wall surface and the innerwall 641 of the outer cylinder or stator of 1 millimeter, a wavelength Lof 4.8 millimeters, and a wavelength, h, of 1 millimeter. For both thesimulations for the smooth wall embodiment and the wavy wall embodiment,a flow rate, q, equal to 13.1 milliliters per minute, and a Taylornumber, Ta, equal to 100 are assumed.

While the embodiment of FIG. 14(a) illustrates a wavy rotor, it shouldbe understood that the inner wall configurations of the outer wallsurface of the rotor 605 and the inner wall surface of the outercylinder or stator 640 can be reversed, meaning that the outer wallsurface 606 of the rotor may be smooth and the inner wall surface of theouter cylinder or stator may be corrugated. The flow patterns for such areversed embodiment in which the outer cylinder or stator has a wavywall inner surface and the outer wall surface of the rotor is smoothwill look the same as illustrated in FIGS. 15(a) and (b). Additionally,one skilled in the art would recognize that walls of both the rotor andstator of the present reactor that form the annular fluid gap may becorrugated. One skilled in the art would further recognize that thecorrugated surface of the wavy wall embodiment need not have sharpalternating peaks and valleys. Instead, for example, the peaks andvalleys may be rounded, parabolic, u-shaped, or the like.

The area under the two curves in FIG. 16 should be about the same(approximately=1.0). Thus, the higher the peak, the smaller the width ofthe curve. Usually one takes the width at ½ the height of the curve tocharacterize the curve. In the case of the curve on the right of FIG. 16representing the wavy rotor embodiment the width of the curve at about ½its height is less than about 0.01 log₁₀ D. In an exemplary embodimentthe desired penetration depth of the radiation in the annular fluid gapis equal to approximately the boundary layer thickness of the fluid inthe gap.

It should be emphasized that the above-described embodiments of thepresent disclosure, particularly, any “preferred” embodiments, aremerely possible examples of implementations, merely set forth for aclear understanding of the principles of the invention. Many variationsand modifications may be made to the above-described embodiment(s)without departing substantially from the spirit and principles of thepresent disclosure. All such modifications and variations are intendedto be included herein within the scope of this disclosure and thepresent invention and protected by the following claims.

1. A method for disinfecting an edible fluid comprising: providing afluid reactor including an annular wall having an inside wall surface; arotor having an outer wall surface placed within the annular wall, theinside wall surface of the outer annular wall and the outer wall surfaceof the rotor forming an annular fluid channel; as least one of theinside wall surface of the annular wall and the outer wall surface ofthe rotor having a corrugated surface; a fluid inlet in the outerannular wall in communication with the annular fluid channel; a fluidoutlet in the outer annular wall also in communication with the annularfluid channel; introducing an edible fluid comprising a micro-organisminto the annual fluid channel; controlling the rotation of the rotor toprovide Taylor-Couette vortices in the fluid in the annular fluidchannel; and irradiating the fluid in the annular fluid channel with ananti-microbial amount of energy.
 2. The method of claim 1, furthercomprising the step of establishing laminar Taylor-Couette vortices inthe fluid within the reactor.
 3. The method of claim 2, wherein theTaylor-Couette flow comprises a plurality of circumferential vorticeswithin the annular fluid channel.
 4. The method of claim 1, wherein theenergy source is a lamp for providing ultraviolet light.
 5. The methodof claim 1, wherein the fluid comprises wastewater.
 6. The method ofclaim 1, wherein the edible fluid comprises milk, fruit juice, or abeverage.
 7. The method of claim 1, wherein the ratio of penetrationdepth of the energy to the velocity boundary layer is less than about 1.8. The method of claim 1, wherein the ratio of penetration depth of theenergy to the velocity boundary layer is from about 0.5 to about
 1. 9.The method of claim 1, wherein the fluid reactor comprises a pluralityof fluid annular channels.
 10. A method of disinfecting a fluidincluding an organism comprising: passing the fluid between two surfacesat least one of the surfaces having a corrugated surface; formingTaylor-Couette vortices in the fluid, wherein the fluid has a fluid flowhaving a Taylor number such as to provide laminar vortices; andirradiating the fluid with an anti-microbial amount of energy.
 11. Themethod of claim 10, wherein the anti-microbial amount of energy is about400 J/m².
 12. The method of claim 11, wherein the Taylor number is fromabout 75 to about
 125. 13. The method of claim 11, wherein the organismcomprises bacteria, fungi, protozoa, viruses, or a combination thereof.14. The method of claim 11, wherein the energy is electromagneticenergy.
 15. The method of claim 11, wherein the fluid compriseswastewater.
 16. The method of claim 11, wherein the fluid comprises anedible fluid.
 17. The method of claim 16, wherein the ratio ofpenetration depth of the energy to the velocity boundary layer is lessthan about
 1. 18. The method of claim 11, wherein the ratio ofpenetration depth of the energy to the velocity boundary layer is fromabout 0.5 to about
 1. 19. The method of claim 11, further includingrotating at least one of the surfaces such that the axis of rotation ofthe surface is substantially parallel to the flow of the fluid, whereinthe Taylor number is between about 40 to about 400.